1. Technical Field
The present invention relates to an electro-optical device such as a liquid crystal display device including, for example, a first substrate, a second substrate facing the first substrate, with a sealing material interposed between the first and second substrates, and a liquid crystal layer placed in at least an effective pixel region between the first and second substrates, a manufacturing method thereof, and an electronic apparatus such as a liquid crystal projector having the electro-optical device.
2. Related Art
As widely known in the art, as one example of electro-optical devices, a liquid crystal display device has a structure where a liquid crystal layer is interposed between two substrates, each substrate being formed of a glass substrate, a quartz substrate or the like, a plurality of switching elements, such as thin-film transistors (TFTs), and a plurality of pixel electrodes are arranged in the form of a matrix on one of the two substrates, and a counter electrode is formed on the other of the two substrates. In the above-constructed liquid crystal display device, an image is displayed when an optical characteristic of the liquid crystal layer interposed between the two substrates is varied according to an image signal applied to the liquid crystal layer.
That is, when the image signal is supplied to the plurality of pixel electrodes (formed of indium tin oxide (ITO)) arranged in the form of a matrix through the switching elements such as TFTs and a voltage based on the image signal is applied to the liquid crystal layer between the pixel electrodes and the counter electrode, the alignment of liquid crystal molecules is varied. Accordingly, transmittance of the pixels is varied, and then, light that passes through the pixel electrodes and the liquid crystal layer is varied according to the image signal for display of an image.
In addition, an element substrate on which the TFTs are formed and an opposite substrate facing the element substrate are separately manufactured, and thereafter, are bonded together by means of, for example, a sealing material, which is applied circumferentially, with high precision (for example, within an alignment error of 1 μm) in a subsequent panel assembly process.
In the panel assembly process, first, alignment layers, which are made of, for example, polyimide, to align liquid crystal molecules along substrate surfaces are formed on surfaces of contact between the manufactured element substrate and opposite substrate and the liquid crystal layer. Thereafter, the alignment layers are fired and then rubbed to align the liquid crystal molecules with no application of voltage.
Next, the liquid crystal layer is interposed between the element substrate and the opposite substrate using a liquid crystal sealing method, for example. Specifically, the sealing material is circumferentially applied as an adhesive in a sealing material application region on one of the element substrate and the opposite substrate, with a liquid crystal injection hole formed in a portion of the sealing material. The element substrate and the opposite substrate are bonded together using the sealing material, and then, aligned with each other, compressed and cured. Thereafter, liquid crystals are injected through the liquid crystal injection hole formed in the portion of the sealing material, and then the liquid crystal injection hole is sealed by a sealant thermally cured, thereby completing assembly of the liquid crystal display device.
Such an assembly process of the liquid crystal display device, which is well known in the art, is disclosed in JP-A-9-222612 (hereinafter referred to as Patent Document 1), for example. Patent Document 1 proposes a sealant forming process in which a sealant is prevented from being peeled from an element substrate due to a crack occurring in the sealant by heat generated when the sealant is thermally cured by forming a sealant peel prevention pattern formed of a transparent electrode between the sealant and the element substrate, thereby improving the humidity resistance of the liquid crystal display device.
In the proposed sealant forming process, for example, after an alignment layer is formed on a surface of contact between the element substrate and a liquid crystal layer, a portion of the alignment, which is formed outside of an effective pixel region disposed in a region surrounded by the sealing material, is formed on a planarized insulating layer, which is made of, for example, silicon dioxide (SiO2), boron silicate glass (BSG, i.e., boron-doped oxide film), boron phosphosilicate glass (BPSG, i.e., boron phosphate-doped oxide film) or the like and formed below the alignment layer.
However, since the alignment layer formed of polyimide does not adhere well to the insulating layer formed of the above-mentioned material, humidity penetrates into the effective pixel region through a gap between the insulating layer and the alignment layer while the assembled liquid crystal display device is used under high humidity conditions, which results in deterioration of the humidity resistance of the liquid crystal display device and hence deterioration of picture quality due to display spots.
In addition, in the process of rubbing the alignment layer, rubbing spots may appear such as stripes attached to a display region due to dust particles of the alignment layer the insulating layer when the alignment layer is rubbed.
The above problems are not limited to the insulating layer and also arise due to poor adhesion between the alignment layer and a layer formed below the alignment layer. However, the liquid crystal display device disclosed in Patent Document 1 does not consider the above problems. Accordingly, there is a need to improve the humidity resistance of the liquid crystal display device.
On the other hand, for display of an image in a liquid crystal display device, since incident light passes through not only a liquid crystal layer but also pixel electrodes and a counter electrode, it is desirable to increase transmittance of the pixel electrodes and the counter electrode in order to obtain higher picture quality. For example, JP-A-2005-140836 (hereinafter referred to as Patent Document 2) discloses a technique in which optical thin films, which are formed of, for example, nitride films, are attached immediately below pixel electrodes and a counter electrode, which are formed of ITO films, for increasing the transmittances of the pixel electrodes and the counter electrode.
However, the technique disclosed in Patent Document 2 also has a problem of deterioration of humidity resistance of the liquid crystal display device due to poor surface adhesion between the optical thin films formed of nitride films or the like and the alignment layer made of polyimide or the like.